1. Field of the Invention
The present invention generally relates to a light source unit. More specifically, the present invention relates to a light source unit for a surface-emitting device
2. Background Information
With LEDs (Light Emitting Diodes) employed in a light source unit for a surface-emitting device, individual differences in a production stage cause variation in chromaticity or luminous flux. In the case of a liquid crystal display module, such variation reaches a level at which a difference in contrast or color is clearly discernible by observing the display. Therefore, during manufacturing of a surface-emitting device with a built-in light source unit that uses LEDs as a light source, a ranking is applied to the large number of LEDs by using the chromaticity coordinates of a chromaticity diagram (xy chromaticity diagram in the CIE color system) from the International Commission on Illumination. A ranking is also applied in accordance with luminous flux values in the same manner for luminous flux (lm).
Conventionally, the LED chromaticity (CIE), luminous flux (lm), and forward voltage (Vf) specifications are finely restricted in order to make the emission color variation or the luminance of a surface-emitting device as uniform as possible. A light source unit in which a large number of LEDs having varying chromaticity or luminous flux are mixed together (mixing) is also sometimes used as a measure for making the emission color variation or the luminance as uniform as possible. In this approach, a mixing method is employed whereby LEDs having different chromaticity, luminous flux, and forward voltage specifications are aligned in alternating fashion.
A measure has been proposed for increasing the utilization rate of supplied LEDs having variation in the manufacture of a backlight (e.g., a surface-emitting device) for a liquid crystal module (see Japanese Laid-Open Patent Application Publication No. 2008-147563, for example). Various researches have also been conducted for reducing variation in emission color (see Japanese Laid-Open Patent Application Publication Nos. 2009-158903 and 2001-222242, for example).